A silicon carbide single crystal has characteristics of high withstand voltage and high electron mobility. Therefore, the crystal is expected to use for a power device semiconductor substrate. The silicon carbide single crystal is formed by a single crystal growth method referred as a sublimation method (i.e., a modified Lely method).
The modified Lely method is described as follows. A raw material of silicon carbide is disposed in a graphite crucible, which is almost closed and sealed. A seed crystal is mounted on an inner wall of the graphite crucible in such a manner that the seed crystal faces the raw material. The raw material is heated up to a predetermined temperature between 2200° C. and 2400° C. so that a sublimation gas arises. Temperature of the seed crystal is set to be lower than that of the raw material by a predetermined temperature between several tens degrees C. and several hundreds degrees C. so that the sublimation gas is re-crystallized on the seed crystal. Thus, the silicon carbide single crystal is grown.
The modified Lely method has a limitation of amount of the single crystal, which can be grown by the method, since the raw material of the silicon carbide is reduced in accordance with crystal growth of the silicon carbide single crystal. Therefore, even if additional raw material is added during the crystal growth, it is difficult to manufacture the high quality single crystal continuously. That is, because the silicon carbide sublimes in such a manner that a ratio of Si/C in the sublimation gas exceeds 1. When the additional raw material is added during the crystal growth, the concentration of the sublimation gas in the crucible is changed. Therefore, the change of the concentration disturbs to grow the high quality single crystal.
On the other hand, a prior art of epitaxial growth method of silicon carbide by using a CVD (i.e., chemical vapor deposition) method is disclosed in Published Patent Application, Japanese Translation of PCT International Application No. H11-508531 (i.e., U.S. Pat. No. 5,704,985). FIGS. 20 and 21 are schematic cross sectional views showing manufacturing equipment according to the prior art. As shown in FIG. 20, a susceptor 101 is disposed in a center of a casing 100. The casing 100 and the susceptor 101 are cylinders, respectively. The susceptor 101 is made of high purity graphite and the like. A silicon carbide single crystal substrate 102 as a seed crystal is disposed on an upper end of the susceptor 101. A heating means 103 is disposed outside of the casing 100 at a predetermined position, which corresponds to an outer periphery of the susceptor 101. The heating means 103 heats a raw material gas. Outside around the susceptor 101 is filled with porous graphite 104 as a heat insulation. A passage 105 having a funnel shape is formed in the heat insulation (104). The passage 105 is disposed on a lower end of the susceptor 101. A raw material gas introduction pipe 106 is disposed on a lower end of the casing 100. The pipe 106 supplies the raw material gas including Si and C, which are necessitated for the crystal growth of the silicon carbide single crystal. Another passage 107 is disposed on the upper end of the susceptor 101. The passage 107 is used for discharging the raw material gas. An outlet passage 108 is disposed on an upper portion of the casing 100. The outlet passage 108 connects to an outside of the casing 100. In the manufacturing equipment having the above construction, the raw material gas supplied through the raw material gas introduction pipe 106 passes through the passage 105 formed in the heat-insulation (104). Then, the gas is led into the susceptor 101, and then the gas is heated by the heating means 103. Thus, the silicon carbide single crystal is grown from the seed crystal (i.e., the substrate 102) by the epitaxial growth method. After that, a residual raw material gas passes through the passage 107 disposed on the upper end of the susceptor 101 and passes through the outlet passage 108 disposed on the upper portion of the casing 100, so that the gas is discharged.
Further, another equipment is disclosed in the prior art, as shown in FIG. 21. In FIG. 21, a growth space is provided by a susceptor 200 and a cover 201. The susceptor 200 has a circumference wall. The raw material gas as a raw material is introduced into the growth space so that a crystal growth is performed at a predetermined temperature, at which the substrate 202 begins to sublime. A part of the raw material gas, which does not contribute to the crystal growth, is discharged to the outside of the equipment through a gas outlet 203.
In the method shown in FIGS. 20 and 21, a ratio of Si/C can be kept at a constant ratio during the crystal growth. Therefore, the single crystal having high quality can be grown with a high speed growth rate.
However, in the above method, the whole susceptors 101, 200 are heated at the same temperature, respectively (i.e., the susceptor 101, 200 is heated uniformly). Therefore, the raw material gas introduced into the growth space deposits the single crystal not only on the substrate but also on the inner wall of the susceptors 101, 200. Therefore, when a single crystal having a long length is required to obtain, a growth yield of the single crystal becomes smaller. Further, the growth space and/or the gas outlet (i.e., the passage 107 or the gas outlet 203) are closed with the deposited crystal (that is not unexpected to deposit around the gas outlet), so that the crystal growth cannot be performed stationary. Further, a part of the raw material gas of the silicon carbide, which does not contribute to the crystal growth, discharges to the outside of the susceptors 101, 200, so that the silicon carbide is deposited in discharge passages (i.e., the outlet passage 108 or the gas outlet 203). Therefore, the discharge passage may be plugged so that the crystal growth cannot be performed stationary.
Further, a part of the raw material gas (a non-reacted raw material gas), which does not contribute to crystal growth in the susceptor 101, is absorbed in the heat-insulation 104, so that a poly crystalline silicon carbide is deposited. Therefore, heat insulation performance of the heat insulation 104 is deteriorated. That deterioration may cause an emission path such as the passage 107 and the outlet passage 108 to be plugged. Then, supply of the raw material gas stops so that the continuous crystal growth is prevented.